Submersible caissons and their applications

ABSTRACT

The invention relates to a submersible caisson adapted for use in the construction of sea or river works, of the kind comprising a bottom, at least one lateral wall and a dividing-up device for liquid ballast forming a cellular structure in section substantially parallel to said bottom. The said dividing-up device is a structure completely independent of the wall and the bottom of the caisson which can thus be calculated precisely in accordance with the applied stresses. Many alternative forms of construction are given and the applications referred to are fluid-storage reservoirs, dykes, breakwaters, quay walls, lock walls, dam elements, etc.

United States Patent [191 Gerin June 17, 1975 1 SUBMERSIBLE CAISSONS ANDTHEIR APPLICATIONS [76] Inventor: Gerald Gerin, 4| Avenue Egle,

Maisons-Lafitte, France, 78600 [22] Filed: Feb. 2, 1973 [21] Appl. No.:329,087

[52] US. Cl. 61/46; 61/465; 61/48;

[51] Int. Cl E02d 5/00; 502d 23/02 [58] Field of Search 61/50, 52, 46,46.5, 81,

61/3, 4',206/DIG. 30,46 FR; 217/27, 35; 220/15 [56] References CitedUNITED STATES PATENTS 655,883 8/1900 Middleby, Jr 206/D1G. 30

875,699 1/1908 Dumais 61/46 1,049,221 12/1912 Frankignoul 61/501,149,877 3/1915 Ward 217/35 3,091,089 5/1963 Gellerstad 61/46 PrimaryExaminer-Jacob Shapiro Attorney, Agent, or FirmYoung & Thompson 1 1ABSTRACT The invention relates to a submersible caisson adapted for usein the Construction of sea or river works, of the kind comprising abottom, at least one lateral wall and a dividing-up device for liquidballast forming a cellular structure in section substantially parallelto said bottom. The said dividing-up device is a structure completelyindependent of the wall and the bottom of the caisson which can thus becalculated precisely in accordance with the applied stresses.

Many alternative forms of construction are given and the applicationsreferred to are fluid-storage reservoirs, dykes, breakwaters, quaywalls, lock walls, darn elements, etc.

19 Claims, 21 Drawing Figures PATENTEBJUM 11 m5 3.889.476

SHEET 2 72 21 Y 21 K IZZZI 5 I 22 27 4 y i UL A 11 t I EL JJZI FIG. 4

PATENTEIIJUN 17 I975 13 8 89 ,476

SHEET 4 FIG. 10

SHEET PATENTEDJUN 1 7 I975 mm mm NR QI PATENTEDJUN l 7 I975 SHEET FIG.75

FIG. 18

FIG. 76

SHEET PATENTEIJJUN 17 I975 SUBMERSIBLE CAISSONS AND THEIR APPLICATIONSThe present invention relates generally to sinkable or submersiblecaissons capable of use in the construction of sea or river water-worksand is also directed to the sea or river water-works built by means ofsuch caissons.

The sinkable caissons utilized at the present time for sea or riverworks generally comprise a bottom and a lateral wall, and it is usual toprovide them with a partitioning system forming a cellular structure insection substantially parallel to said bottom.

This partitioning arrangement has generally a double purpose, namely onthe one hand to reinforce the actual structure of the caisson, and onthe other hand to divide or split-up the liquid ballast which pours intothe caisson, thereby ensuring it suitable static and dynamic stabilityin the vicinity of a given position of trim, known as the normal trim,especially during its placing in position.

In the constructional techniques known at the present time, thispartitioning device is incorporated in the caisson, which may offer theadvantage of simplicity but which presents the disadvantage that it doesnot dissociate the two functions which it carries out.

The result of this is especially that the actual wall of the caisson isrequired to withstand forces which are practically of the same order asthose of the partitioning system, that it is practically impossible toemploy a relatively thin wall for the caisson in view of the forcesintroduced into this wall by the partitioning system which is fixed init here and there, and that it is finally difficult to adapt thethickness of these elements correctly to the forces which are applied toit at a given depth of immersion.

These drawbacks become increasingly important as the depth of submersionof the caisson considered increases.

There have of course been proposed various types of special caissonscomplying with various specific requirements.

Some of these special caissons, intended to form the walls of quays aredesigned in such manner as to be capable of being tilted on thefloat-line before they are submerged. They have a relatively complexstructure with an inclined rear face formed by a large number of arches.

Other special caissons are more particularly designed in order to formunder-water tanks to be submerged to great depths.

Finally, other special caissons are made of cylinders joined together,each having as its bottom a thin dome capable of being eliminated aftersubmerging, by means of explosive charges.

The common feature of all these special caissons is that they have thedrawbacks briefly specified above, essentially due to the fact thattheir partitioning system forms an integral part of the caisson.

The present invention has generally speaking for its object to overcomethis drawback.

More precisely, it has first of all for its object a sinkable caissonfor sea or river water-works of the kind comprising a bottom, at leastone lateral wall and a device for dividing-up the liquid ballast,forming a cellular structure in section substantially parallel to thesaid bottom, characterized in that the said dividing-up device is is astructure independent of the said wall and of the said bottom.

it has also for its object a dividing device of this kind, takenseparately.

it has finally for its object a sea or river water-works of any kindcomprising at least one sinkable caisson utilizing or having utilized adividing device of this type.

The dividing-up system according to the invention forms a structureentirely separate from that of the caisson, and thus it does notintroduce into the walls of this latter any forces or stresses otherthan those resulting directly from the presence of a liquid ballast inthe interior of this partitioning system. The thickness of the caissonwalls can then be calculated very accurately and can in the majority ofcases be substantially reduced as compared with the thickness ofcomparable sinkable caissons known at the present time.

in addition, the partitioning device according to the invention beingindependent of the caisson in which it is fitted, it may be removableand if so desired could be recovered for a fresh use.

In most cases, it is however sufficiently cheap to be abandoned, if sodesired in the final work constituted by the caisson when this latter isin position.

Furthermore, the partitioning device according to the invention hasgenerally only a low weight and it therefore only raises very little thecentre of gravity of the caisson in which it is installed, It may thusoccupy in such a caisson only a substantially lower height than incomparable sinkable caissons known at the present time, this heightbeing measured from the bottom of the caisson.

In addition, the dividing-up arrangement according to the invention doesnot interefere in any substantial manner with the play of the thrust andabutment forces on the lateral wall of the caisson of the final ballast,generally of sand, which ensures it stability after submersion.

Furthermore, the dividing-up arrangement according to the inventionrenders possible the construction of cylindrical caissons, the wall ofwhich is only coupled to the associated bottom by anisotropic means,such as hooped synthetic rubber supports, preferably in combination inthis case with flexible fluid-tight sealing means.

The dividing-up device according to the invention also makes it possibleto produce caissons the lateral wall of which is, over at least part ofits height, doubled by a second wall which is associated with the samebottom as the first, but which is quite free of any mechanical couplingwith the first, the annular space thus formed permitting for example theplacing in position of a final ballast, and ensuring in all cases animproved protection of the caisson against possible shocks.

Other advantages result from the fact that the caisson, which mayespecially be made of pre-stressed reinforced concrete, is free at itsfinal stage from any rigid internal partitioning, which for examplefacilitates the placing in position of the final ballast, aftersubmerging.

However this may be, the dividing-up device according to the inventionmay be presented in numerous forms of construction.

It may for example bear directly against the walls or the bottom of thecaisson.

In an alternative form, it may only bear on the wall and/or the bottomof the caisson by a lattice network of rolls radially deformable underpressure.

In all cases, the device has preferably relative deformability withrespect to the wall of the caisson, such that the pressure of a liquidballast contained therein is transmitted in a substantially uniformmanner to the said wall.

In a simplified form, the dividing-up device according to the inventionmay be formed by an assembly of partitions which are substantiallyperpendicular to the bottom of the caisson, and which plunge into arelatively impermeable bed of material resting on the said bottorn.

In addition, according to another aspect, the dividing-up deviceaccording to the invention may be in one piece or it may be composed ofa number of distinct parts separable from each other.

As has been mentioned above, the present invention has also for itsobject a sea or river water-works comprising at least one submersiblecaisson of the type briefly described above.

It may be concerned, for example, with a fluid storage reservoir, anembankment, a breakwater, a quay wall, a side wall of a lock, a darnelement, etc.

More particularly, in the case of a fluid storage reservoir, the wall ofthis reservoir is preferably formed by an upward extension of the wallof a submerged caisson of the type such as briefly described above, andits bottom is preferably formed by a flexible fluid-tight layer restingon a sandy ballast placed on the bottom of the said caisson.

Reservoirs of this kind enable the product which is stocked in them tobe kept out of direct reach of a shock damaging their supportingstructure.

They may furthermore be utilized under the same conditions as a landreservoir of the same capacity, especially as regards the pumping of theproduct stored.

In addition, they may be equipped with a conventional floating roof.

In the case of a breakwater, this may comprise according to theinvention a plurality of similar sinkable caissons located at a distancefrom each other.

The cylindrical shape of these caissons, combined with the empty spacesexisting between them, generally permits an effective damping of theswell in a very open sector centered on a perpendicular to the workconstituted by such an association of caissons, while limiting theamplitude of the ripple complex in front of a work of this kind to avalue definitely lower than that of the normal lapping amplitude.

The characteristic features and advantages of the invention will furtherbe brought out in the description which follows below, given by way ofexample, reference being made to the accompanying diagrammatic drawings,in which:

FIG. 1 is a view in vertical section of a caisson according to theinvention during the course of its submersion, this cross-section beingtaken along the line I-I of FIG. 2;

FIG. 2 is a view in transverse section of this caisson, taken along theline II-II of FIG. 1;

FIG. 3 is a view on a larger scale in partial crosssection of thiscaisson, taken along the line III-III of FIG. 2.

FIG. 4 is a view similar to FIG. 2, and relates to an alternative formof construction;

FIGS. 5 to 8 are partial views in vertical cross-section of thisalternative form, taken respectively along the lines V-V to VIIIVIII;

FIG. 9 is a view similar to FIG. 8 and illustrates a working phase ofthe partitioning device according to the invention;

FIG. 10 is a view in vertical cross-section illustrating the placing inposition by immersion of a caisson according to the invention;

FIG. 11 is a view in vertical cross-section of a storage reservoirformed by means of a caisson of this kind;

FIG. 12 is a partial view to a larger scale and in verticalcross-section of this reservoir;

FIG. 13 is a view in elevation and in cross-section illustrating aninstallation comprising a number of these reservoirs;

FIG. 14 is a plan view of an installation of this kind;

FIG. 15 is a view in vertical cross-section of a simplifled form ofconstruction of a partitioning device according to the invention;

FIG. 16 is a view in partial axial cross-section to a larger scale of acaisson according to the invention;

FIG. 17 is a partial view in transverse cross-section of this caisson,taken along the line XVIIXVII of FIG. 16;

FIG. 18 is a view similar to FIG. 16 and relates to an alternative formof construction;

FIG. 19 is a view similar to FIG. 15 and concerns an alternative form ofconstruction;

FIG. 20 is a view of this alternative form in crosssection taken alongthe line XXXX of FIG. 19;

and FIG. 21 is a view similar to FIG. 12 and relating to anotheralternative form of construction.

FIGS. 1 and 2 relate to a caisson comprising generally a bottom 10 and acylindrical lateral wall 11. In the example shown, the transversesection of this caisson is square and the thickness of its wall 11decreases gradually from its bottom.

According to the invention, with this caisson is associated an internaldividing-up system 12, formed by a plurality of partitions 13substantially perpendicular to the bottom 10, the said partitions 13forming in section parallel to this bottom a cellular structure.

Each of the cells 14 of this structure is fluid-tight with respect tothe adjacent cells.

According to the form of construction shown, the partitions 13 whichform these cells are incorporated in a common bottom 15, and thedividing-up device 12 thus constituted only bears against the bottom 10and the wall 11 of the caisson by means of a lattice system of rolls 16.

These rolls or tubes 16 are preferably inflatable, is so desired, byindependent sections, from an inflation system 17.

These rolls 16 are formed by radially deformable casings which aresubstantially inextensible. In FIG. 2 their crossing has been shownlevel with a junction of the cellular structure constituted by thepartitioning device 12.

The rolls or tubes 16 have a double purpose. On the one hand they ensurea contact between the dividingup device 12 and the caisson, and on theother hand, they divide-up the space existing between these elements inorder to minimize the movements of the ballast water in this space withrespect to the period of oscillation of the whole unit.

However this may be, it is important that the dividing-up device 12should not have any considerable movement with respect to the caisson,which could give rise locally to excess pressures liable to effect thislatter adversely. It is also important that the levels of ballast waterin each of the cells 14 of the dividing-up device 12 do not differ fromeach other, for the whole of the cells, by more than a height lower thana previously fixed limit, the actual strength of the partitions 13 ofthis dividing-up device being calculated as a function of this limit.

The rolls or tubes 16 inherently act in opposition to any movement ofthe dividing-up device 12 with re spect to the caisson. but in analternative construction this function could be effected by anyappropriate fixing means, and for example by means of tenons which fixtogether the bottoms and 15.

As regards the levels in the cells 14, in order to control them, theremay be available at the base of each wall or partition 13 of thedividing-up device, two clapper-valves working in opposite directionsfrom one cell 14 to the adjacent cell, the said clapper-valves or otherone-way flow devices (not shown) being calibrated or set in such manneras to operate when the difference in pressure between the cells inquestion reaches a predetermined value, taking account of suitablecoefficients of safety.

In practice, the rolls 16 are inflated to a pressure higher than thatwhich will be applied to them by the liquid ballast placed in positionin the dividing-up device 12 during the immersion of the caisson.

These rolls 16 thus transmit to the caisson only the forces which aredirectly associated with the mass of this ballast.

As will be readily understood, and as shown in FIG. I, this ballastgradually introduced into the dividing-up device 12 permits theprogressive placing in position of the caisson up to its immersion, thedividing-up device permitting a suitable trim of the said caisson to bemaintained by partitioning this ballast.

Once the caisson has been sunk, the dividing-up device may be eliminatedif so desired and it may eventually be recovered for a fresh use.

According to the alternative construction illustrated in FIGS. 4 to 7and more particularly intended for cylindrical caissons of large sizeand circular section, the dividing-up device 12 according to theinvention rests on a bed of sand 20 which forms a ballast ensuring agood stability of the bottom of the caisson on the waterline, withoutballast, and several similar portions 21 are formed six in number in theexample shown, these having generally the form of circular segments.

The portions 21 are separable from each other and are movable.

These portions 21 have as before a cellular structure and are arrangedaround a central well 22. This well is provided with a cover 23 whichalso ensures the central junction of the said portions 21.

As can better be seen from FIG. 6, the upper adjacent edges of twoadjacent portions 21 are covered in pairs by a joint cover 25.

On the periphery, the dividing-up device 12 is coupled to thecylindrical wall II of the caisson by two flexible skirts. one 28 comingfrom the upper edge of the portions 21 and held applied against the wall11 of the caisson by an inflatable circular tube 29, or any otherdevice, the other, 30, coming from the base of the portions 21, andbeing applied against the wall ll of the caisson by the liquid ballastintroduced into the dividing-up device 12.

The flexible skirt 30 forms with the peripheral cells I3, an annularspace which is partitioned and which communicates with the saidperipheral cells by passages 26 located at the base of the correspondingwalls 13.

Similarly, around the well 22, the end cells 27 of the portions 21communicate with the adjacent cells by similar passages 26.

As will be readily understood, the flexible skirt 28 prevents anyinsertion of liquid ballast between the dividing device 12 and the wallll of the caisson, when this liquid ballast is delivered by pumping overthis wall. This liquid ballast is therefore first of all confined by thecells of the dividing device 12 during all the operations whilefloating, and then, when the caisson is submerged and the fillingcontinues, these cells becoming almost full, the liquid ballast poursinto the caisson by the central well 22 which then acts as an overflow.

There is thus a progressive movement of this liquid ballast into thesand ballast 20, followed by its insertion from the top to the bottombetween the flexible skirt 30 and the wall 11 of the caisson (see FIG.9) which ensures automatic detachment of this flexible skirt 30 withrespect to the wall 11 of the caisson.

FIGS. 10 and 12 illustrate the application of the invention to theestablishment of a fluid-storage reser voir, for example a tank forhydrocarbons.

FIG. 11 illustrates more precisely the submerging phase of the caissonintended to form the reservoir body, this submersion being effected bymeans of a dividing device 12 according to the invention, which rests ona sand ballast 20, and in which submerged pumps 35 gradually deliver theballast water.

After submerging (see FIG. 11) the caisson is partly filled with a finalsandy ballast 36, passages or drainage channels 37 being provided in thewall 11 of the caisson so as to allow the hydrostatic levels to becomebalanced as far as possible on each side of this wall.

A flexible sealing layer 38 is then placed in position on the sandballast 36, in co-operation with an annular sealing joint 39, as shownin FIG. 12.

Thus, as can be seen from FIG. 12, air vents 40 are provided in the wall11 for the breathing of the sand ballast 36.

The fluid 41 to be stored is put into position directly on the flexiblesealing layer 38, so that the storage reservoir 51 thus formed has itswall constituted by the upward extension of the wall 11 of the caisson,and its bottom is formed by the flexible fluid-tight layer 38 placed inposition on the sandy ballast of the caisson.

The roof of such a reservoir may be formed, without any particulardifficulty, by a conventional floating roof 43 of the same type as thoseemployed on reservoirs built on land.

Furthermore, such a sea or river tank offers the same possibilities ofexploitation as a reservoir installed on land. These possibilities areillustrated in FIGS. 11 and 13. In this latter figure, there have beenshown dia grammatically at 45 the incoming and outgoing pipe conduits,at 46 the service bridges, at 47 a technical construction and at 48 alanding quay.

As shown in FIG. 14, an installation of this kind may serve a number ofstorage reservoirs 51 of the same type as that described above, thesereservoirs being for example arranged substantially in line andeventually forming a dyke.

These reservoirs offer the maximum safety in respect of pollution, sinceonly a major shock can cause a leakage of the stored fluid.

In the case where such reservoirs are effectively required to form adyke, it may be advantageous to arrange them at a distance from eachother in order that their circular shape, combined with the empty spacesbetween them. can enable the best compromise to be obtained between asmall agitation on the sheltered side and an admissible over-elevationon the exposed side.

FIG. 15 illustrates a simplified form of construction of the dividingdevice 12 according to the invention. This latter is then simply formedby an assembly of inter-crossed walls 55 which are substantiallyperpendicular to the bottom 10 of the caisson and which plunge into abed of relatively permeable material 56 arranged on this bottom 10.

In fact, this bed 56 must be made of a sufficiently impermeable materialin order that percolation may not be too rapid, especially during therocking movements of the caisson due to the swell.

The dividing device according to the invention furthermore permits aparticular construction of the caisson, in which it is intended to beplaced.

This possibility is illustrated in FIGS. I6 to 18; the bottom 10 of thecaisson is an apron distinct from the associated wall 11, this wallresting on the bottom on simple supports 60.

These supports are preferably made of anisotropic material capable oftransmitting the direct forces, but not their moments. Supports of thiskind may be made of hooped synthetic rubber and especially of rubbersold under the Trade name of NEOPRENE."

According to the form of construction shown in FIG. 16, an annularfluid-tight joint 61, of the WATERSTOP type for example, is associatedwith the supports 60, a packing of elastic material 62 is insertedbetween the peripheral edge of the bottom or apron l and the wall 11,and the latter is engaged by a shoulder 63 on the bottom or apron 10.

This shoulder may have a section with a circular contour, or asaw-toothed contour as illustrated in FIG. 17.

According to the alternative form shown in FIG. 18, the wall 11 restssimply by its edge on the bottom or apron with the interposition ofsupports 60 of anisotropic material, these supports being associatedwith one or more annular fluid-tight joints 61.

FIGS. 19 and 20 relate to an alternative form of construction in whichthe caisson is provided parallel to its bottom 10 with a polygonalsection, for example an octagonal section.

FIG. 21 illustrates a further possibility offered by the invention,especially for the construction of reservoirs of the same type as thatdescribed with reference to FIGS. 10 to 12.

According to the form of construction shown in FIG. 21, the wall 11 ofthe caisson is doubled by a second wall 70 arranged coaxially oreccentrically about the previous wall, the two walls 11 and 70 beingassociated with the same bottom or apron 10, but being free from anymechanical connection with each other.

The annular space 71 between these two walls can be advantageouslyemployed for placing in position the sand or other ballast at a levelwhich may be different from that of the sand ballast in the internalspace.

However this may be, the additional wall provides further protection forthe caisson.

It will of course be understood that the present invention is notlimited to the forms of construction described and illustrated, butincludes any alternative form of construction and/or of combination oftheir various elements. In all cases, the dividing-up device willpreferably be established in such manner as to have a relativedeformability with respect to the wall of the caisson such that thepressure of a liquid ballast contained therein is transmitted in asubstantially uniform manner to the said wall, or a capacity of movementsuch that there is practically no transmission of force radially andaxially. In this case the partitions may for example be slidably mountedin grooves formed in the wall of the caisson.

What I claim is:

1. An offshore caisson of prestressed reinforced concrete for use in theconstruction of sea or river works, comprising a sea-worthy structureincluding a bottom, at least one lateral wall, and means for dividing upliquid ballast in the caisson comprising, in section sub stantiallyparallel to the bottom, a cellular structure independent of said walland said bottom, and means supporting said cellular structure in spacedrelation from said wall and said bottom.

2. An offshore caisson as claimed in claim I, wherein the dividing upmeans is removable from the rest of the caisson.

3. An offshore caisson as claimed in claim 1, said supporting meanscomprising a radially deformable system of rolls in lattice formation,said dividing up means bearing against the wall and the bottom of thecaisson only through said radially deformable system.

4. An offshore caisson as claimed in claim 1, wherein the dividing upmeans comprises a plurality of partitions substantially perpendicular tothe bottom of the caisson, and a bed of relatively impermeable materialon said bottom, said partitions projecting into said bed.

5. An offshore caisson as claimed in claim 1, wherein said dividing upmeans comprises a plurality of distinct, separable parts.

6. An offshore caisson as claimed in claim 5, further comprising a flatcover strap for holding the upper edges of said parts together in pairs.

7. An offshore caisson as claimed in claim 5, further comprising acentral wall, said parts being disposed around the central wall whichacts as an overflow de vice.

8. An offshore caisson as claimed in claim 5, wherein the parts aresurrounded by at least one flexible cylindrical skirt, furthercomprising holding means for exerting said skirt against the lateralwall of the caisson.

9. An offshore caisson as claimed in claim 8, further comprising a firstflexible skirt at the top of said dividing up means, and an inflatabletube or roll for urging said flexible skirt against the lateral wall ofthe caisson.

10. An offshore caisson as claimed in claim 9, further comprising asecond flexible skirt at the base of said dividing up means, said secondflexible skirt being urged against the lateral wall of the caisson byliquid ballast.

11. An offshore caisson as claimed in claim 1, wherein the lateral wallis cylindrical and is joined to said bottom only by anisotropic means incombination with flexible sealing means.

12. An offshore caisson as claimed in claim 1, in which the lateral wallis covered, over at least part of its height, by a second wall which isassociated also with said bottom and has no mechanical connection withthe first lateral wall.

13. An offshore caisson as claimed in claim 1, wherein said dividing upmeans is relatively deformable with respect to the lateral wall of thecaisson so that the pressure of liquid ballast therein is transmitted tothe lateral wall in a substantially uniform manner.

14. An offshore caisson as claimed in claim 1, further comprisinggrooves in the lateral wall, said dividing up means having a pluralityof partitions slidably mounted in the grooves.

15. An offshore construction comprising a plurality of offshore caissonsas claimed in claim 1.

16. An offshore caisson as claimed in claim 1, for use in theconstruction of a fluid storage reservoir, wherein said lateral wall ofthe caisson forms the side wall of the reservoir. further comprising asandy ballast on said bottom of the cassion and a fluidtight layersupported on the sandy ballast forming the bottom of the reservoir.

17. A breakwater comprising a plurality of caissons according to claim 1spaced apart from one another.

18. An offshore caisson as claimed in claim 1, in the form of a buoyantvessel, and means for introducing ballast into said vessel to alter thebuoyancy thereof.

19. An offshore caisson as claimed in claim I, wherein said dividing upmeans comprises a single unitary structure.

1. An offshore caisson of prestressed reinforced concrete for use in theconstruction of sea or river works, comprising a seaworthy structureincluding a bottom, at least one lateral wall, and means for dividing upliquid ballast in the caisson comprising, in section substantiallyparallel to the bottom, a cellular structure independent of said walland said bottom, and means supporting said cellular structure in spacedrelation from said wall and said bottom.
 2. An offshore caisson asclaimed in claim 1, wherein the dividing up means is removable from therest of the caisson.
 3. An offshore caisson as claimed in claim 1, saidsupporting means comprising a radially deformable system of rolls inlattice formation, said dividing up means bearing against the wall andthe bottom of the caisson only through said radially deformable system.4. An offshore caisson as claimed in claim 1, wherein the dividing upmeans comprises a plurality of partitions substantially perpendicular tothe bottom of the caisson, and a bed of relatively impermeable materialon said bottom, said partitions projecting into said bed.
 5. An offshorecaisson as claimed in claim 1, wherein said dividing up means comprisesa plurality of distinct, separable parts.
 6. An offshore caisson asclaimed in claim 5, further comprising a flat cover strap for holdingthe upper edges of said parts together in pairs.
 7. An offshore caissonas claimed in claim 5, further comprising a central wall, said partsbeing disposed around the central wall which acts as an overflow device.8. An offshore caisson as claimed in claim 5, wherein the parts aresurrounded by at least one flexible cylindrical skirt, furthercomprising holding means for exerting said skirt against the lateralwall of the caisson.
 9. An offshore caisson as claimed in claim 8,further comprising a first flexible skirt at the top of said dividing upmeans, and an inflatable tube or roll for urging said flexible skirtagainst the lateral wall of the caisson.
 10. An offshore caisson asclaimed in claim 9, further comprising a second flexible skirt at thebase of said dividing up means, said second flexible skirt being urgedagainst the lateral wall of the caisson by liquid ballast.
 11. Anoffshore caisson as claimed in claim 1, wherein the lateral wall iscylindrical and is joined to said bottom only by anisotropic means incombination with flexible sealing means.
 12. An offshore caisson asclaimed in claim 1, in which the lateral wall is covered, over at leastpart of its height, by a second wall which is associated also with saidbottom and has no mechanical connection with the first lateral wall. 13.An offshore caisson as claimed in claim 1, wherein said dividing upmeans is relatively deformable with respect to the lateral wall of thecaisson so that the pressure of liquid ballast therein is transmitted tothe lateral wall in a substantially uniform manner.
 14. An offshorecaisson as claimed in claim 1, further comprising grooves in the lateralwall, said dividing up means having a plurality of partitions slidablymounted in the grooves.
 15. An offshore construction comprising aplurality of offshore caissons as claimed in claim
 1. 16. An offshorecaisson as claimed in claim 1, for use in the construction of a fluidstorage reservoir, wherein said lateral wall of the caisson forms theside wall of the reservoir, further comprising a sandy ballast on saidbottom of the cassion and a fluidtight layer supported on the sandyballast forming the bottom of the reservoir.
 17. A breakwater comprisinga plurality of caissons according to claim 1 spaced apart from oneanother.
 18. An offshore caisson as claimed in claim 1, in the form of abuoyant vessel, and means for introducing ballast into said vessel toalter the buoyancy thereof.
 19. An offshore caisson as claimed in claim1, wherein said dividing up means comprises a single unitary structure.